The present invention relates generally to ice protection devices and deals more particularly with an ice suppression mat for preventing an ice formation from adhering to and the subsequent jacking out or pushing over of a marine pile or like object as a result of vertical and lateral forces developed by the ice formation.
Severe damage may be caused to marine piles, boats, piers, docks and like objects which are partially submerged in a body of water subject to natural icing conditions. Such conditions occur, for example, in the Northeast and Great Lakes regions of the United States where fresh and brackish water routinely freezes over coastal waters. As the water freezes, an ice plate or sheet forms and collects on or adheres to objects in the water. Powerful vertical and lateral forces are exerted on those objects when there is a change in water level or horizontal ice expansion. Tests have shown that ice can withstand a force perpendicular to the ice surface of 500-1100 PSI and a force parallel to the ice surface of 250-900 PSI before compressive failure occurs.
When an object, such as, for example, a marine pile is frozen in a sheet of ice and the water level changes due to tidal and/or seiche action, the buoyancy of the ice sheet exerts vertical forces on the pile until the ice either breaks or overcomes adhesion to the pile and slides up. In many instances, the ice sheet surrounding the pile does not break or lose its hold and lifts the pile from the sea bed as the water level rises and returns it to its original position when the water level falls. However, sand or mud often fills the hole beneath a pile lifted by the ice during a high water level so that the pile cannot return to its original position when the water level falls. The repeated action of lifting a pile and filling its hole will jack the pile upward causing the pile to be at an elevation that is higher than its initial elevation. In some cases, the pile may be pushed over by lateral forces as the ice expands horizontally and in some instances, may be jacked completely out of its hole in the sea bed whereupon a structure, for example, such as a pier or dock, supported by the pile may collapse or be extensively damaged. Single pile applications such as small boat anchors and single pile navigational aids are also subject to being destroyed or removed and lost due to the ice forces which jack them out. The result of this damage is high repair costs to re-drive piles and re-build piers or other structures.
It is well known that the density of water decreases as it cools until it reaches 4 degrees Celsius at which time as cooling continues, the water expands so that the colder water floats above the warmer water strata below and it is this well recognized phenomenon which causes water to freeze from the surface downwardly. Obviously, the water in the lower strata must be above freezing at all times otherwise this water would freeze in the same manner as the surface water. Consequently, ice formation can be prevented by insulating the surface of the water from the colder air above it.
There have been many devices proposed and utilized to prevent ice from forming on marine piles. These devices, however, have not proved to be completely cost effective or otherwise satisfactory because they are often difficult to place in position or have limited applications.
One means for preventing ice damage has been by the use of a network of tubes which lay on the water's bottom and are supplied with compressed air to create air bubbles throughout the area to be maintained ice free. The air bubbles rise toward the surface bringing the lower, warmer water to the surface where it combines with the colder surface water to raise its temperature above freezing. The bubble system is effective in preventing ice formation but it is relatively expensive to purchase and operate and subject to corrosion and other degradation resulting from prolonged submergence, particularly in highly saline waters. The bubble system is also restricted to areas where electricity is available and consequently, cannot generally be used in remote areas.
U.S. Pat. No. 3,370,432 issued to Butler discloses a sheath surrounding a piling to be protected wherein an antifreeze solution is placed bewtween the piling and the sheath so that ice cannot form around the piling. The sheath will rise and fall with the tide, however, such apparatus is generally dropped in position over the top of the pile prior to the placement of a structure thereon. The antifreeze is also subject to dissipation as it is absorbed by the pile or otherwise dispersed.
U.S. Pat. No. 3,317,299 issued to Clark discloses a device in the form of a sheath situated around a pile and extending from above the high water line to well below the point at which ice freezes. An insulating material is carried in a ring at the upper portion of the sheath and extends from slightly above the water surface to a depth below that at which ice is expected to freeze so that heat is conducted by the sheath from the lower warmer water strata to the upper colder water strata and prevents freezing.
U.S. Pat. No. 3,180,099 issued to Mikolajczyk, et al discloses a pile protector in the form of a vertically slidable sheath positioned around a pile and containing an inner lining of material having a low coefficient of friction. The sheath extends below the point at which ice forms and also above the high water line. A spring is placed between the top of the sheath and the bottom of a dock or pier supported by the pile and thus, when ice is frozen around the sheath and the tide is rising, the sheath moves upwardly and compresses the spring. When the tide lowers, the spring returns the sheath to its original position and therefore, the sheath moves up and down around the pile preventing any upward force on the pile itself.
The Dow Chemical Company has conducted experiments utilizing a large foam mat in a dockside area to insulate the water below the mat from the colder air above and prevent ice formation in a large area adjacent to a dock. The mat, however, was difficult to place in position and anchor. In addition, the mat was not able to resist damage caused by high winds.
Accordingly, it is the general aim of the present invention to provide an effective and economical ice suppression mat for preventing ice formations from collecting on and jacking out a pile.
It is another aim of the present invention to provide an ice suppression mat that is easy to use with single or multiple pile configurations and with pilings having structures attached thereto.
A further aim of the present invention is to provide an ice suppression mat that is effective over a wide range of ice depths.
Other features and advantages of the invention will become apparent from the following written description and the drawings forming a part thereof.